1) Field of the Invention
This invention relates generally to an apparatus for cleaning disc like elements such as silicone wafers. More specifically, the present invention relates to an apparatus for cleaning and rinsing silicone wafers in the semiconductor process industry.
2) Prior Art
In the process of manufacturing integrated semiconductor circuits or semi-conductor devices using a semiconductor wafer, various impurities tend to be defused onto the surface of the wafers. Metalization, deposition, diffusion and etching processes on the wafers thereafter can be affected by the impurities. For example, metalization layers can be affected to the point that, electrical pathwaves intended to be formed by the metalization layer may be severely reduced in size or even completely blocked by the impurities. This results in either malfunctioning of the integrated circuit in the case of a short circuited electrical pathways, or impairment resulting in eventual malfunctioning due to heating and eventual shorting of a partially blocked electrical pathway.
In the case of a deposition process, impurities on the wafer surface can cause irregular or oxide growth, resulting in "lumpiness" of the deposition layer.
Also, in the case of diffusion processing of wafers, impurities such as inorganic particulates can cause deflection of the layering material resulting in an uneven diffusion layer.
It is necessary therefore prior to forming metalization, deposition, diffusion, etc., layers on semi-conductor wafers, to take steps to free the wafer surfaces of solid matter, films, chemical impurities and solvents which may have been absorbed during prior steps in the manufacturing process.
Further, it is often an important part of the rinsing process to complete the eching stop of a previous process. The ech stop must be reliable and must be completed within a predictable time period. It is therefore necessary to be able to monitor impurity levels corresponding to the amount of echant present in the rinsing apparatus in order to insure a proper etch stop.
Several prior art processes have been developed to clean and rinse wafers prior to further processing operations. These processes have been discussed in applicant's co-pending patent application entitled "METHOD FOR CLEANING AND RINSING WAFERS", application Ser. No. 07/561,805, and now U.S. Pat. No. 4,997,490, the disclosure of which is incorporated herein by reference.
Many attempts have been made to develope apparatus' useful for performing cleaning and rinsing processes. These devices have been developed and used with only limited success however. Such prior art devices generally include a chamber into which a plurality of wafers have been located. The chamber is then either completely filled with a fluid such as deionized water and quickly emptied (dumped) with the filling and emptying being repeated a preset number of cycles. Alternatively the chamber has been fitted with a means of spraying water or steam, or the like against the wafers in such a manner as to dislodge particular impurities. Other prior art devices employ similar chambers to allow water to continuously flow past the wafers to remove the impurities (usually referred to as Cascade-type rinsers), and may include the use of megasonics in conjunction with the fluid flow.
There has been no suggestion of an apparatus for cleaning and rinsing wafers which is capable of long and repeated sequences of cycles which involve the use of a tank for holding a plurality of wafers, with the tank being capable of filling and dumping, with subsequent simultaneous cascading and spraying of water over the top of the tank.
Further there has been no suggestion to develop a tank type apparatus which allows a partial dump of the water in the tank to allow for useful exchange of fresh water thereinto while preventing the wafers therein from being exposed to air.
Further the development of an apparatus which can perform a sequence of full water dump steps, in combination with partial dumps and/or full cascading steps including a delayed spray step to minimize the liquid/air interface with the wafers has yet to be suggested. The minimization of exposure of wavers to air limits the potential oxide regrowth and particulate contamination therefrom. The combination of cascading and spraying with partial dumping of the tank, which has yet to be suggested in the prior art, allows for sprays to remove the light weight contaminates from the surface of the tank, while at the same time allowing for partial dumps to remove heavy contaminates from the bottom of the tank.
Also, there has been no suggestion to combine each of these capabilities into a tank apparatus which also includes the ability to monitor any one of a number of characteristics including chemical characteristics, corresponding to the level of contaminates within the tank water. Further, this has never been successfully performed with a monitor which is isolated from the tank so as to avoid the introduction thereby of contaminates which can subsequently become deposited on the wafers.
Further, there has been no suggestion to measure the characteristics of the water which correspond to contaminates therein, for the purpose of controlling the operation of the rinsing and cleaning cycles of the apparatus in such a manner as to optimize the effectiveness thereof, and minimize the total volume of water, consumed thereby.